[CentOS] Re: ATA-over-Ethernet v's iSCSI -- CORAID is NOT SAN, also check multi-target SAS

Nick Bryant list at everywhereinternet.com
Wed Nov 9 23:24:35 UTC 2005

> On Nov 8, 2005, at 5:19 AM, Bryan J. Smith wrote:
> > On Tue, 2005-11-08 at 15:16 +1100, Nick Bryant wrote:
> >
> >> When I said shared storage I didn't mean it had to be accessed at
> >> the same
> >> time from all hosts. The RHEL cluster suite in an active/standby
> >> setup
> >> actually mounts the partitions as a host changes from standby to
> >> active after its sure the active host hasn't got access anymore
> >> with a
> >> "lights out" OoB setup.
> >> Well that was my understanding of how it worked anyhow?
> >
> > Yes, but you're missing a key point.  The system designated for
> > failover
> > is still mounting the volume -- even if by standby.  Think of it as a
> > "read-only" mount that tracks changes done by the other system with
> > the
> > "read/write" (I know this is a mega-oversimplification).  And when it
> > does fail-over, it still has to be allowed to mount it when the other
> > system may be in a state that the target device believes is still
> > accessing it.
> Just one additional point. RH cluster suite requires (at least it did
> in RHEL3 clustering) two shared raw partitions to store state
> information and (I believe) some heartbeating.
> This blows AoE out for anything with the cluster suite.
> RedHat Clustering (again in 3), does not mount both volumes
> simultaneously for normal services however. When a node fails over,
> it is forcibly umounted on one system and remounted on the other.
> This means you can use ext3 with cluster suite. But the point above
> leads you to need a block level device.

Of course, the quorum partition. Oh well that answers that one....

It looks like a low cost angle isn't going to happen for now. Bal*s.

Thanks for all the feedback.

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